The effect of acoustic speed variations, i.e., inhomogeneous index of refraction, on ultrasonic reflection tomography is examined by computer simulation and experiment. The result shows that the resolving power of reflection tomography is lowered and structural distortions are caused by acoustic speed variations even in the case of small refractive index fluctuations, as in biological objects. A method based on transmission time-of-flight measurements is developed to correct this refraction effect, and its validity was experimentally verified for a test phantom and dog hearts.
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